So just finished that storage fill/wipe. I got a reset once during the process when the tablet locked up at about 150MB storage free, after the reboot I restarted the process, got down to 0.10MB free, and everything seems to be working well now. While my write speeds (as per Androbench) hadn't dropped below their normal 10.5MB/s sequential, it's notable that my then 83 IOPS random are now up at 128 IOPS random after the storage wipe. So even if you're not seeing much real lag, but occasional hesitancy it may be worth filling and deleting your empty storage.
Going to make a quick PSA post for those suffering the lag so they see this.